fix: show better error messages

docs/index.md

@@ -93,10 +93,17 @@ You can use `snapshot(x)` like you can use `x` in your assertion with a limited
 !!! warning
     One snapshot can only be used with one operation.
     The following code will not work:
+    <!-- inline-snapshot: show_error outcome-failed=1 -->
     ``` python
-    s = snapshot(5)
-    assert 5 <= s
-    assert 5 == s  # Error: s is already used with <=
+    def test_something():
+        s = snapshot(5)
+        assert 5 <= s
+        assert 5 == s
+
+
+    # Error:
+    # >       assert 5 == s
+    # E       TypeError: This snapshot cannot be use with `==`, because it was previously used with `x <= snapshot`
     ```
 
 ## Supported usage

inline_snapshot/_inline_snapshot.py

@@ -86,6 +86,7 @@ def snapshot_env():
 class GenericValue:
     _new_value: Any
     _old_value: Any
+    _current_op = "undefined"
 
     def _needs_trim(self):
         return False
@@ -116,8 +117,34 @@ def get_result(self, flags):
     def __repr__(self):
         return repr(self._visible_value())
 
+    def _type_error(self, op):
+        __tracebackhide__ = True
+        raise TypeError(
+            f"This snapshot cannot be use with `{op}`, because it was previously used with `{self._current_op}`"
+        )
+
+    def __eq__(self, _other):
+        __tracebackhide__ = True
+        self._type_error("==")
+
+    def __le__(self, _other):
+        __tracebackhide__ = True
+        self._type_error("<=")
+
+    def __ge__(self, _other):
+        __tracebackhide__ = True
+        self._type_error(">=")
+
+    def __contains__(self, _other):
+        __tracebackhide__ = True
+        self._type_error("in")
+
+    def __getitem__(self, _item):
+        __tracebackhide__ = True
+        self._type_error("snapshot[key]")
 
-class Value(GenericValue):
+
+class UndecidedValue(GenericValue):
     def __init__(self, _old_value):
         self._old_value = _old_value
         self._new_value = undefined
@@ -131,7 +158,7 @@ def _needs_fix(self):
     # functions which determine the type
 
     def __eq__(self, other):
-        self._change(FixValue)
+        self._change(EqValue)
         return self == other
 
     def __le__(self, other):
@@ -151,7 +178,9 @@ def __getitem__(self, item):
         return self[item]
 
 
-class FixValue(GenericValue):
+class EqValue(GenericValue):
+    _current_op = "x == snapshot"
+
     def __eq__(self, other):
         other = copy.deepcopy(other)
 
@@ -228,6 +257,8 @@ class MinValue(MinMaxValue):
 
     """
 
+    _current_op = "x >= snapshot"
+
     @staticmethod
     def cmp(a, b):
         return a <= b
@@ -251,6 +282,8 @@ class MaxValue(MinMaxValue):
 
     """
 
+    _current_op = "x <= snapshot"
+
     @staticmethod
     def cmp(a, b):
         return a >= b
@@ -259,6 +292,8 @@ def cmp(a, b):
 
 
 class CollectionValue(GenericValue):
+    _current_op = "x in snapshot"
+
     def __contains__(self, item):
         item = copy.deepcopy(item)
 
@@ -300,6 +335,8 @@ def get_result(self, flags):
 
 
 class DictValue(GenericValue):
+    _current_op = "snapshot[key]"
+
     def __getitem__(self, index):
         if self._new_value is undefined:
             self._new_value = {}
@@ -309,7 +346,7 @@ def __getitem__(self, index):
             old_value = {}
 
         if index not in self._new_value:
-            self._new_value[index] = Value(old_value.get(index, undefined))
+            self._new_value[index] = UndecidedValue(old_value.get(index, undefined))
 
         return self._new_value[index]
 
@@ -487,7 +524,7 @@ def triple_quote(string):
 class Snapshot:
     def __init__(self, value, expr):
         self._expr = expr
-        self._value = Value(value)
+        self._value = UndecidedValue(value)
 
     @property
     def _filename(self):

tests/test_inline_snapshot.py

@@ -2,6 +2,7 @@
 import itertools
 import textwrap
 from collections import namedtuple
+from contextlib import nullcontext
 from dataclasses import dataclass
 from dataclasses import field
 from typing import Set
@@ -840,3 +841,22 @@ def test_format_value(check_update):
 
 def test_unused_snapshot(check_update):
     assert check_update("snapshot()\n", flags="create") == "snapshot()\n"
+
+
+def test_type_error(check_update):
+    tests = ["5 == s", "5 <= s", "5 >= s", "5 in s", "5 == s[0]"]
+
+    for test1, test2 in itertools.product(tests, tests):
+        with pytest.raises(TypeError) if test1 != test2 else nullcontext() as error:
+            check_update(
+                f"""
+s = snapshot()
+assert {test1}
+assert {test2}
+        """,
+                reported_flags="create",
+            )
+        if error is not None:
+            assert "This snapshot cannot be use with" in str(error.value)
+        else:
+            assert test1 == test2

tests/test_pytest_plugin.py

@@ -507,6 +507,10 @@ def test_docs(project, file, subtests):
                 if flags:
                     new_code = project.source
 
+                if "show_error" in options:
+                    new_code = new_code.split("# Error:")[0]
+                    new_code += "# Error:" + textwrap.indent(result.errorLines(), "# ")
+
                 if (
                     inline_snapshot._inline_snapshot._update_flags.fix
                 ):  # pragma: no cover
@@ -523,6 +527,7 @@ def test_docs(project, file, subtests):
                         assert {
                             f"outcome-{k}={v}"
                             for k, v in result.parseoutcomes().items()
+                            if k in ("failed", "errors", "passed")
                         } == {flag for flag in options if flag.startswith("outcome-")}
                     assert code == new_code
                 else:  # pragma: no cover